.The markings inside the helmet indicate that it belonged to the Prussian Guard /Dragoon which did have a horse artillery unit
some expert who wrote the seller said:Only the 1st, 2nd, 3rd and 4th Wurttemburg Feldartillerie Regts had this shape brim & a cruciform base, but they had a different front plate (Wurttemburg shield with stag and lion).
argonne said:I think that some expert who wrote the seller wrote, maybe just wanted the "Pickelhaube circle" to explain, that this haube probably is a Württemberg Feldartillerie helmet, wich original Württ. frontplate has been once upon a time replaced by this Guard eagle plate......???? Not sure at all about the experts intention...